The present embodiments relate to programmable electrical fuses for use in integrated circuits and are more particularly directed to integrated circuits that include an array configuration of such fuses.
Programmable fuses exist in the art in at least two forms, a first known as a laser fuse and a second known as an electrical fuse. For both types, each fuse is either left intact to provide a first logical state or is “programmed” so that the fuse is opened, effectively by destroying a portion of the fuse structure so that its conductivity path is opened, to provide a second logical state which is complementary of the first logical state. In the case of a laser fuse, a laser is used to open each selected fuse by physically imparting the laser energy to the fuse, thereby destroying the continuity of the fuse and providing an open circuit across it. In the case of an electrical fuse, a relatively large amount of current is flowed through the fuse, thereby destroying the continuity of the fuse and providing an open circuit across it. Another type of electrical fuse is referred to in the art as an anti-fuse, where an affirmative action is taken to restore connectivity through the fuse to obtain a first data state, or this act is not taken with respect to the fuse in order to provide a second and complementary data state. In either event, such fuses and the states they provide have been used for various applications. For example, these programmable fuses may be used for memory redundancy control, integrated circuit die identification, analog trimming control, customer configuration bits, encryption key coding, as well as other applications.
Also in the prior art, both laser and electrical fuses are located in distributed locations across an integrated circuit die. For example, U.S. Pat. No. 6,292,422, entitled “Read/Write Protected Electrical Fuse,” issued Sep. 18, 2001, assigned to Texas Instruments Incorporated, and hereby incorporated herein by reference, illustrates such an approach. In some implementations of this nature, typically each fuse is proximate other circuitry that requires the digital value provided by the corresponding fuse. Moreover, typically a storage device is associated with each such fuse and, thus, these storage devices are also distributed at different locations across the integrated circuit. Further, to evaluate if the fuses are properly programmed, the distributed storage devices can be read from the device as a scan chain. Often during the manufacturing process, only selected ones of the fuses are opened according to a technique as described above, thereby causing them to provide one logic state while the unaffected fuses provides another and complementary logic state. To accomplish the programming of selected fuses, therefore, the efforts to selectively destroy only those selected fuses also must be made at locations distributed across the die. Moreover, with respect to electrical fuses, there is required that additional fuse blowing circuitry, including what is sometimes referred to as a zap transistor in connection with each separate fuse, also must be distributed across the die. Also with respect to electrical fuses, there is required that a corresponding circuit for reading each fuse, such as a sense amplifier or comparable circuitry for comparing the fuse voltage with a reference voltage, must be distributed across the die for each respective fuse.
While the current state of the art has provided various useful implementations, the present inventors have observed that while the prior art has improved upon previous systems, there remains still additional improvements as provided with respect to various issues in the preferred embodiment. For example, various considerations arise from the distributed nature of the prior art approach. Such considerations include increased complexity when circuit design changes are made, a lack of scalability, and increased complexity and signal drive requirements in sufficiently routing power to fuses for programming and for reading an entire scan chain at a time to determine if the fuses have been correctly programmed. Other issues exist in that certain additional aspects are not provided or cannot be provided as compared to the preferred embodiments. Accordingly, there arises a need to address the drawbacks of the prior art and to provide still additional functionality and benefits as compared to prior art programmable fuses architectures, where such aspects will be further appreciated from the remaining teachings of this document.